My first class after intro was Galatians. The book really stuck with me through the years, so I would also recommend it for a Pauline starter. We used Hendricksen's commentary (ca.1968) or a reprint in 1977. Galatians is an emotive-packed epistle. Those strong feelings of the author will help you internalize the Greek (it's not like reading the geneologies or narratives - Paul contains neither genre, but does talk about his past actions in a narrative fashion which is easier to read.) The text is in your face and confrontational. It contains numerous rhetorical devices, μέν...δέ constructions, numerous imperatives, rhetorical questions, contrary to fact statements, etc., quotations from the OT and midrash on them. So it has more features than shorter works like Philemon.
Make sure you get a good commentary, nowadays there is an NIGTC (New International Greek Testament Commentary) by F.F. Brucehttp://www.amazon.com/Epistle-Galatians-International-Testament-Commentary/dp/0802823874
. Also the Word Biblical Commentary 41
by Longenecker http://www.amazon.com/Word-Biblical-Commentary-Vol-Galatians/dp/0849902401/
. Both of those will deal with the Greek text. The old ICC commentary by William De Witt Burton https://play.google.com/store/books/details?id=e1Q2h5tCWv8C&rdid=book-e1Q2h5tCWv8C&rdot=1
. I'm not sure what are the criticisms of any of these commentaries, but they all deal with the Greek text. Neither Mounce's Graded Reader nor Deckert's Koine Reader contain any passages from Galatians.
Other commentaries are
Fung, Ronald Y. K. The Epistle to the Galatians. New International Commentary on the New Testament. Grand Rapids: Wm. B. Eerdmans, 1988 (ISBN: 987-0802825094. $38.00).
Martyn, J. Louis. Galatians. Yale Anchor Bible. New Haven, CT: Yale University Press, 1997 (ISBN: 978-0300139853. $50.00).
Schreiner, Thomas R. Galatians. Zondervan Exegetical Commentary on the New Testament. Grand Rapids: Zondervan, 2010 (ISBN: 978-0310243724. $34.99).
Perhaps someone can chime in about which commentary they feel is best suited for the Greek beginning-intermediate student for Galatians. On the other hand, there is a Baylor Handbook on the Greek Text for Ephesians. http://www.baylorpress.com/Book/19/Ephesians.html
. None yet for Galatians.